1. Field of the Invention
The present invention is related to a multilayer structure employed in a hybrid IC (integrated circuit) or a semiconductor device, etc. More particularly, it is related to connection of the electrically conductive layers insulated by a resin layer therebetween.
2. Description of the Related Arts
There have been employed many kinds of multilayer structures and their fabrication methods for fabricating hybrid ICs (integrated circuit) or semiconductor devices. A typical one of them is Japanese Unexamined Patent Publication Sho-61-22693 shown in FIGS. 1a-1c. In this method, an insulative layer 34 is coated over an electrically conductive pattern 33 formed on an insulative substrate 31; and a via hole 34a is opened on a predetermined position of insulative layer 34 as shown in FIG. 1a. Via hole 34a is then filled with a metal material by either electroplating or electroless plating so that a via 35 is formed therein as shown in FIG. 1b. A second electrically conductive pattern 36 is formed over thus fabricated insulative layer 34, as shown in FIG. 1c.
This method, however, causes problems as described hereinafter. That is, it requires a very long time, such as more than 24 hours, for forming the 20 .mu.m thick via in the via hole by electroless plating. The required time can be reduced by employing electroplating; however, not only the via top uneven relative to the surface of insulative layer 34 but also there remains a mechanical stress at the connection of second pattern 36 and peripheral part of via 35 after second pattern 36 is formed, resulting in a possibility of causing disconnection thereof. This is because a photosensitive polyimide resin employed for insulative layer 34 has a thermal expansion coefficient widely different from that of the metal material of via 35. Therefore, another problem is also caused in that the via does not adequately adhere to the insulative layer. Resulting from these problems, the reliability of the connection between the multilayers has not been satisfactory.
In order to avoid the mismatch problem of the thermal expansion coefficients, an employment of a non-photosensitive polyimide resin can be considered; however, it is disadvantageous that this material requires a metal mask or a resist which is resistant to plasma, which requires a complicated fabriation process, resulting in the deterioration of the process reliability.